[PATCH 4/8] target/arm: Don't allow RES0 CNTHCTL_EL2 bits to be written

[Peter Maydell <peter.maydell@linaro.org>]

Don't allow the guest to write CNTHCTL_EL2 bits which don't exist.
This is not strictly architecturally required, but it is how we've
tended to implement registers more recently.

In particular, bits [19:18] are only present with FEAT_RME,
and bits [17:12] will only be present with FEAT_ECV.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
 target/arm/helper.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/target/arm/helper.c b/target/arm/helper.c
index 1c82d12a883..8ec61c12440 100644
--- a/target/arm/helper.c
+++ b/target/arm/helper.c
@@ -2968,6 +2968,24 @@ static void gt_cnthctl_write(CPUARMState *env, const ARMCPRegInfo *ri,
 {
     ARMCPU *cpu = env_archcpu(env);
     uint32_t oldval = env->cp15.cnthctl_el2;
+    uint32_t valid_mask =
+        R_CNTHCTL_EL0PCTEN_MASK |
+        R_CNTHCTL_EL0VCTEN_MASK |
+        R_CNTHCTL_EVNTEN_MASK |
+        R_CNTHCTL_EVNTDIR_MASK |
+        R_CNTHCTL_EVNTI_MASK |
+        R_CNTHCTL_EL0VTEN_MASK |
+        R_CNTHCTL_EL0PTEN_MASK |
+        R_CNTHCTL_EL1PCTEN_MASK |
+        R_CNTHCTL_EL1PTEN_MASK;
+
+    if (cpu_isar_feature(aa64_rme, cpu)) {
+        valid_mask |= R_CNTHCTL_CNTVMASK_MASK | R_CNTHCTL_CNTPMASK_MASK;
+    }
+
+    /* Clear RES0 bits */
+    value &= valid_mask;
+
     raw_write(env, ri, value);
 
     if ((oldval ^ value) & R_CNTHCTL_CNTVMASK_MASK) {
-- 
2.34.1